The invention pertains to the field of arc fault detectors and interrupters, and in particular, to an arc fault interrupter which detects and interrupts upstream and downstream series arcing and downstream parallel arcing, while detecting upstream parallel arcing in order to prevent tripping.
A percentage of fires each year are caused by electrical branch circuit wiring arcing faults involving currents below the trip level of a conventional circuit breaker or OCPD (over current protection device) as well as below the handling rate of the breaker. Basic overcurrent protection afforded by circuit breakers is designed to prevent I2R heating of the wiring in the electrical distribution system, caused by circuit overloading or line-to-line faults, and not necessarily arcing faults. A true short circuit is a rarity in an electrical system. In fact, it is more accurate to think of electrical faults as having some level of impedance, such as a high impedance arc fault (low current) or a low impedance fault (high current). Many electrical faults begin as high impedance breakdowns between the line and neutral conductors or to the ground wire or device components. AFCI (Arc Fault Circuit Interrupter) technology affords protection from conditions that may not necessarily be an immediate threat but could become hazardous if left unattended.
In order to start a fire, three elements must be present fuel, oxygen(air), and energy to ignite the fuel. Arcing is defined as a luminous discharge of electricity across an insulating medium. The electrical discharge of an arc can reach temperatures of several thousand degrees Celsius. Arcing produces sufficient energy to reach the ignition point of nearby combustible material(s) before a circuit breaker can respond. Arc detection is an enhancement to thermal magnetic overload detection typically used in circuit breakers or OCPD""s, which alone may not detect and respond to arc faults.
A number of devices for detecting arc faults and methods of detection have been used in the past. These include using E and B field arc sensors, detecting the amplitude of the rate of change of current signals when an arc fault occurs, using non-overlapping band pass filters to detect white noise characteristic of arcs, and utilizing the high frequency components (RF) of arcing waveforms to detect arcing faults. While some of these techniques are more or less effective than others, they require relatively sophisticated arc sensors and circuits. Heretofore, most arc detection circuits have been incorporated in circuit breakers.
xe2x80x9cA-typexe2x80x9d arc faults are those in which the arc occurs across a break in the line or neutral conductors or at a loose terminal in a branch circuit of a distribution network. The conductors are carrying current to a load derived from the line voltage. The arc could likewise occur as a break or at a loose terminal associated with an extension cord deriving power from line voltage, thereby completing the circuit to the load. Since the current through the A-type fault is limited by the impedance of the load itself, since the fault is in series with the load, an A-type fault is also known as a xe2x80x9cseries fault.xe2x80x9d
B-typexe2x80x9d arc faults are a second arcing condition that must be detected and interrupted by a combination outlet device. In a B-type fault, the arc occurs across two conductors in the branch circuit or extension cords plugged into it, at a site where the insulating media separating the two conductors has been compromised. The arc may occur across the line and neutral conductors or the line and ground conductors, or in the case of reverse polarity where the line voltage is reverse-polarized, between the neutral and ground conductors. The current through the B-type fault is not limited by the impedance of the load, but rather by the available current from the supply established by the impedance of the conductors and terminals between the source of line voltage and the position of the parallel fault, i.e., the conductive members carrying the fault current. Since B-type faults are effectively across the line, they are also known as xe2x80x9cparallel faults.xe2x80x9d
There is a need for simple economical arc fault detectors that can be included in wiring devices such as duplex receptacles, multi-outlet strips, or in-line devices, and that offer the same protection as an arc fault detector incorporated in a circuit breaker but at lower cost. There is a need for an arc fault circuit detector in wiring devices that can be provided at a reduced cost compared with arc fault circuit detecting circuit breakers comparable to the reduction in cost between ground fault interrupting receptacles and ground fault interrupting circuit breakers.
Briefly stated, downstream series and parallel arcing in AC power lines is determined by using a detector and microprocessor to detect characteristic di/dt behavior received from a current sensor through which the power lines pass. When downstream parallel arcing is detected, the microprocessor uses a speedy algorithm which cannot be used to detect series arcing. Upstream series arcing is detected by sensing a flat voltage portion of the line voltage. Upstream parallel arcing is detected by sensing a voltage spike followed by a voltage flat portion of the line voltage. When upstream parallel arcing is detected, the microprocessor is temporarily shut off to avoid false tripping.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes first sensing means for sensing a line current in the AC electric power distribution system and producing a di/dt signal; circuit means for processing the di/dt signal and producing an output; tripping means for interrupting power to the load; processing means for processing the output to determine an existence of a downstream arc fault, the processing means including a normal algorithm and a speedy algorithm for processing the output, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; second sensing means for sensing a sinusoidal load current of a fundamental frequency of the power distribution system above a first predetermined level; circuit means, responsive to the second sensing means, for initiating the speedy algorithm within the processing means; circuit means for detecting an existence of an upstream series arc, and upon detection of the upstream series arc, for signaling the processing means to send the trip signal to the tripping means; and circuit means for detecting an existence of an upstream parallel arc, and upon detection of the upstream parallel arc, for deactivating the processing means so that the processing means does not send the trip signal to the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; first sensing means for sensing upstream arc faults in the AC electric power distribution system and producing an output; processing means for processing the output to determine an existence of a downstream arc fault, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; first circuit means for detecting an existence of an upstream series arc, and upon detection of the upstream series arc, for signaling the processing means to trip the tripping means; and second circuit means for detecting an existence of an upstream parallel arc, and upon detection of the upstream parallel arc, for deactivating the processing means so that the processing means does not send the trip signal to the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electrical power distribution system includes tripping means for interrupting power to the load; sensing means for sensing arc faults in the AC electrical power distribution system and producing an output; processing means for processing the output to determine an existence of a downstream arc fault, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; first circuit means for detecting an existence of an arc fault signal, and upon detection of the arc fault signal, for signaling the processing means to trip the tripping means; and second circuit means for detecting an existence of upstream arc mimicking noise, and upon detection of the upstream arc mimicking noise, for deactivating the processing means so that the processing means does not send a trip signal to the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; sensing means for sensing arc faults in the AC electric power distribution system and producing an output; processing means for processing the output to determine an existence of a downstream arc fault, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; first circuit means for detecting an existence of arc fault signal, and upon detection of the arc fault signal, for signaling the processing means to trip the tripping means; and filter means located upstream of the sensing means; wherein the filter means prevents arc mimicking noise on the AC electric power distribution system from signaling the processing means to trip the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; first sensing means for sensing a line current in the AC electric power distribution system and producing a di/dt signal; circuit means for processing the di/dt signal and producing an output; processing means for processing the output to determine an existence of a downstream arc fault, the processing means including a normal algorithm and a speedy algorithm for processing the output, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; second sensing means for sensing a sinusoidal load current of a fundamental frequency of the power distribution system above a first predetermined level; and circuit means, responsive to the second sensing means for initiating the speedy algorithm within the processing means when the first predetermined level is exceeded for a predetermined interval, wherein the second sensing means includes a shunt resistance in series with the line.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; sensing means for sensing a ground fault current in the AC electric power distribution system; wherein the sensor is connected to a Zener diode, the Zener diode being connected to the tripping means, in which sensed ground fault current by the first sensing means produces a signal which breaks over the Zener diode which in turn activates the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; sensing means for sensing a line current in the AC electric power distribution system, the sensing means including a toroidal transformer in which the line is a primary winding and a secondary winding produces a di/dt signal; circuit means for processing the di/dt signal and producing an output; processing means for processing the output to send a trip signal to the tripping means upon detection of the di/dt signal; circuit means for determining a magnitude of the di/dt signal; and high impedance means responsive to the magnitude, wherein a plurality of di/dt signals greater than a pre-established threshold cause the high impedance means to open, thereby blocking the plurality of di/dt signals from the processing means, and unloading the secondary winding of the sensor.